Acid-Base Status, Renal Function, Water, and Macromineral Metabolism of Dry Cows Fed Diets Differing In Cation-Anion Difference

¹ Department of Animal Science, McGill University, Macdonald Campus, 21,111 Lakeshore Road, Ste-Anne de Bellevue, QC, Canada H9X 3V9

Dietary cation-anion difference was defined as the summation of the milli-equivalents of Na and K minus the sum of the milliequivalents of Cl and S per kilogram of DM. Twelve Holstein cows were used in a crossover experiment to compare the effects of changing the cation-anion difference of a diet based on haylage. Two cation-anion differences, 481.8 and 327.2 meq/kg, were compared. Increased dietary cation-anion difference had no significant effects on BW or intake and digestibility of DM, ADF, NDF, and N. The diet with a cation-anion difference of 481 meq/kg of DM increased apparent absorption of water and urine volume. Fecal excretion of Na and absorption and urinary excretion of S were increased by a cation-anion difference of 327 meq/kg of DM. Although blood concentrations were unaffected, lower dietary cation-anion difference reduced concentration of H⁺ and HCO₃^- in urine and total urinary excretion of HCO₃^-. Plasma volume, packed cell volume, glomerular filtration rate, and effective renal plasma flow were unaffected by diet. Small changes in dietary cation-anion differences, even within the positive range, affected acid-base status and water metabolism of dry pregnant cows without affecting renal function or blood volume.

Key Words: dietary cation-anion difference • acid-base balance • macromineral • renal function

Submitted on January 13, 1994
Accepted on November 11, 1994

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